PTL1 shows, aside from a usual ignition device, an ignition coil including a DC-DC converter which inputs discharge energy to the ignition coil on the secondary side.
The ignition device of PTL1 extends the discharge continuation period after starting discharge by supplying power to an ignition plug through the secondary coil of the ignition coil, and thereby attempts to ensure stable ignition.
However, regarding the conventional ignition device shown in PTL1, because an electric current is directly supplied to the secondary coil of the ignition coil where the extremely high voltage is generated, the DC-DC converter needs to be formed by high-voltage elements. This results in an increase in manufacturing cost, an increase in size of the device, and a decrease in reliability.
In PTL2, a spark plug includes a full-bridge circuit. The full-bridge circuit includes an ignition coil (Tr), a first serially connected circuit having a first switching means (T1) and a second switching means (T2), and a second serially connected circuit having a third switching means (T3) and a fourth switching means (T4). A center tap (1) of the first serially connected circuit is connected to a power source potential, a center tap (2) of the second serially connected circuit is connected to a reference potential, and the first and second center taps are each connected to a primary side of the ignition coil. Further, a capacitor (Cz) and a fifth switching means (T5) connected to the second center tap and a diode (D1) are provided. The ignition device having the following characteristics is shown. That is, a controller device (SE) controls the switching means to cause breakdown, and subsequently to generate an alternating current having a constant amplitude.